Multicarrier signals that are based on OFDM technology such as Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE) signals suffer from high peak-to-average ratio (PAR). These wideband signals are subject to severe in-band and out-of-band distortion when they are transmitted using power amplifiers (PAs) that operate outside their linear range. Since high linearity requirements leads to low power efficiency and, therefore, to high power consumption, processing the signal to reduce the PAR by crest factor reduction (CFR) techniques contribute to increasing the PA efficiency.
Crest factor reduction is typically used in transmitters and helps to linearize the amplifier. CFR is a technique that clips the magnitude of the transmitted signal to a certain level, such as an OFDM signal, to decrease the peak-to-average ratio prior to transmission. There are various schemes of crest factor reduction that can be divided into two main categories: the first does not require receiver side modification. The second does require receiver side modifications. Methods that require receiver side modifications include tone injection, selected mapping, partial transmit, and tone reservation, and such. These schemes are known to be complex (high amount of hardware (field-programmable gate array (FPGA), application-specific integrated circuit (ASIC) resources) and may have good performance (good adjacent channel leakage ratio (ACLR) and good error vector magnitude (EVM)); however, they may not be acceptable if there is a requirement that the receiver must not modify the received signal. Among the schemes that do not require receiver side modifications are schemes based on hard clipping, peak cancellation by windowing and active constellation, and such. These are known to have moderate complexity (moderate hardware resources) and moderate performance (ACLR and EVM) since hard clipping has an adverse effect on the ACLR and windowing has an adverse effect on the EVM.
When hardware resources are low there is a need in the art for an improved crest factor reduction technique. In particular, there is a need for an improved crest factor reduction technique that uses very low hardware resources and delivers good performance (good ACLR and good EVM).